CMP0069

INTERPROCEDURAL_OPTIMIZATION is enforced when enabled.

CMake 3.9 and newer prefer to add IPO flags whenever the INTERPROCEDURAL_OPTIMIZATION target property is enabled and produce an error if flags are not known to CMake for the current compiler. Since a given compiler may not support IPO flags in all environments in which it is used, it is now the project’s responsibility to use the CheckIPOSupported module to check for support before enabling the INTERPROCEDURAL_OPTIMIZATION target property. This approach allows a project to conditionally activate IPO when supported. It also allows an end user to set the CMAKE_INTERPROCEDURAL_OPTIMIZATION variable in an environment known to support IPO even if the project does not enable the property.

Since CMake 3.8 and lower only honored INTERPROCEDURAL_OPTIMIZATION for the Intel compiler on Linux, some projects may unconditionally enable the target property. Policy CMP0069 provides compatibility with such projects.

This policy takes effect whenever the IPO property is enabled. The OLD behavior for this policy is to add IPO flags only for Intel compiler on Linux. The NEW behavior for this policy is to add IPO flags for the current compiler or produce an error if CMake does not know the flags.

This policy was introduced in CMake version 3.9. CMake version 3.19.0-rc3 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

Examples

Behave like CMake 3.8 and do not apply any IPO flags except for Intel compiler on Linux:

cmake_minimum_required(VERSION 3.8)
project(foo)

# ...

set_property(TARGET ... PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)

Use the CheckIPOSupported module to detect whether IPO is supported by the current compiler, environment, and CMake version. Produce a fatal error if support is not available:

cmake_minimum_required(VERSION 3.9) # CMP0069 NEW
project(foo)

include(CheckIPOSupported)
check_ipo_supported()

# ...

set_property(TARGET ... PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)

Apply IPO flags only if compiler supports it:

cmake_minimum_required(VERSION 3.9) # CMP0069 NEW
project(foo)

include(CheckIPOSupported)

# ...

check_ipo_supported(RESULT result)
if(result)
  set_property(TARGET ... PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
endif()

Apply IPO flags without any checks. This may lead to build errors if IPO is not supported by the compiler in the current environment. Produce an error if CMake does not know IPO flags for the current compiler:

cmake_minimum_required(VERSION 3.9) # CMP0069 NEW
project(foo)

# ...

set_property(TARGET ... PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)